1. Field of the Invention
The present invention relates to a high frequency device used for MEMS (Micro Electro Mechanical Systems), and particularly to a high frequency device including a high frequency signal-use analog circuit such as a filter circuit.
2. Description of the Related Art
As an element of a circuit for transmitting and receiving a radio wave of a television, a radio broadcasting, and a wireless LAN, a bandpass filter and lowpass filter are an essential element, and are an important electronic component that largely affects quality of a transmission signal. Examples of representative products in this field include a ceramic filter (for example, Japanese Unexamined Patent Application Publication No. 2007-220874). As a ceramic filter, various products for every frequency band are provided. For example, a SAW (Surface Acoustic Wave) filter is provided in MHz band of a transmitting and receiving circuit of a television and a radio, and a laminated ceramic filter is provided in GHz band of a transmitting and receiving circuit of a wireless LAN and a mobile device.
Though the ceramic filter is a superior device for providing high filter characteristics, the ceramic filter has a disadvantage that the size thereof is large. In recent years, a mobile device such as a mobile phone, a mobile player, and a net PC (Personal Computer) includes function as a television, a radio, and a wireless LAN. Thus, a significantly small filter device with the inherent characteristics has been aspired. Technical innovation of the ceramic filter has progressed, and 0608 size chip type laminated ceramic filter has been commercialized. However, in designing a set equipment, a single digit smaller device has been necessitated.
In addition to the ceramic filter, a sophisticated small filter device has been developed. Example thereof include a filter device formed on a silicon substrate. Along with currently improved high frequency characteristics of a CMOS (Complementary metal oxide semiconductor) circuit, such a filter device formed on the silicon substrate particularly attracts attention. If a desired filter circuit is able to be formed by the CMOS process on the silicon substrate, a combination circuit with other CMOS circuit is enabled, and accordingly a single digit or more smaller circuit than the ceramic filter is able to be realized.
As such a filter device, a high frequency filter circuit has been developed (for example, Japanese Unexamined Patent Application Publication No. 2003-297924). The high frequency filter circuit is provided as part of the high frequency transmission line provided on the surface of a silicon substrate. A signal line, a dielectric thin film formed under the signal line, and the silicon substrate constitute a capacitive device based on a planar pattern, an inductive device, and a resistive device.